The present invention relates generally to magnetic storage apparatus and, more particularly, to high-density magnetic storage devices having the recording density of more than 4 gigabits per square inch (Gbit/in.sup.2). The invention also relates to magnetic recording media of low noise and high reliability with reduced reproduction output attenuation occurring due to thermomagnetic relaxation to attain high-density recordabilities required.
In recent years, as magnetic storage apparatus rapidly increases in recording density, it is demanded to attain high-sensitivity magnetic heads along with advanced magnetic storage media high in magnetic coercive force and yet low in noise. While currently available magnetic head assemblies typically employ a magnetic head of the magnetoresistance effect type, also known as magnetoresistive (MR) heads, an endless demand for increased data storage density calls for accelerated development of further advanced magnetic heads of the giant magnetoresistance (GMR) type which are two or three times greater in sensitivity than standard MR heads.
In addition, as portable or handheld personal computers (PCs) such as "notebook" PCs are sharing larger part in the digital computer market, prior known storage media with an Al--Mg alloy substrate metallized or plated with NiP (referred to as "Al substrate" hereinafter) are being replaced with glass-substrate media having enhanced physical durability or robustness against attendant shocks during hand-carrying or "on-the-fly" usage outside the users' offices, which media are under accelerated development today. Unfortunately, advantages of such glass-substrate media do not come without accompanying a penalty: these tend to decrease in magnetic properties more significantly than conventional Al-substrate media due to defective adherence, immersion or "invasion" of impurity gasses from a substrate into its associative films, degradation of in-plane orientation of magnetization easy axis, increased particle or grain sizes, and others. An approach to avoiding such problem associated with the prior art is to newly form between the substrate and an undercoat layer or underlayer more than one additive layer including an intermediate layer, seed layer, barrier layer and the like. One typical scheme incorporating this principle has been disclosed in, for example, JP-A-1-134913 (laid open on May 26, 1989). A similar scheme is set forth in JP-A-1-134984 (laid open on May 26, 1989). These Japanese documents teach and suggest that the adhesiveness might increase by formation of an intermediate layer which is made of oxide of a chosen metal containing therein at least one element as selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, and Mn, which leads to achievability of good contact-start-stop (CSS) characteristics. In addition, referring to JP-A-4-153910 (laid open on May 27, 1992), it is disclosed therein that formation of an amorphous or micro-crystalline film may enable miniaturization of particle or grain dimensions to thereby reduce the risk of attendant noises, which film is comprised of Y as well as one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W. JP-A-5-135343 (laid open on Jun. 1, 1993) demonstrates the fact that forming on a glass substrate an oxygen isolator layer allows resultant magnetic coercive force to increase, which layer contains therein a chosen rare earth element in addition to one kind of element selected from the group consisting of Ta, Y, Nb and Hf. Reference is further made to JP-A-7-73441 (laid open on Mar. 17, 1995), which indicates obtainability of higher coercive force by forming on a substrate either an amorphous Cr alloy or V alloy because such formation permits a Cr under-layer formed thereon to exhibit the (211) orientation causing a Co-alloy magnetic layer to have the (10.0) orientation with its magnetization easy axis facing the inside of a film surface, i.e. lying parallel to the film surface.